This chapter theoretically explains the electronic structures of open-shell singlet systems with a wide range of open-shell (diradical) characters. The definition of diradical character and its correlation to the excitation energies, transition properties, and dipole moment differences are described based on the valence configuration interaction scheme using a two-site model with two electrons in two active orbitals. The linear and nonlinear optical properties for various polycyclic aromatic hydrocarbons with open-shell character are also discussed as a function of diradical character.

中文翻译：

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开壳单线态分子的电子结构：双基字符观点

本章从理论上解释了具有广泛的开壳（双基）字符的开壳单重态系统的电子结构。基于价构型相互作用方案，使用在两个活动轨道中具有两个电子的两个位点模型，基于价构相互作用方案，描述了双自由基特性的定义及其与激发能，跃迁性质和偶极矩差的相关性。还讨论了具有开壳特征的各种多环芳烃的线性和非线性光学性质，作为双自由基特征的函数。